1. Field of the Invention
The teachings in accordance with exemplary and non-limiting embodiments of this disclosure relate generally to a torque sensor mounted on a vehicle to detect a torque change between an input shaft and an output shaft, and to a torque angle sensor configured to measure changes in rotation angle between an input shaft and an output shaft.
2. Discussion of the Related Art
Generally, almost every vehicle employs an electric power-assist steering system. That is, a steering system that assists a steering force of a vehicle with a separate power is used to enhance the motion stability of a vehicle.
Conventionally, the auxiliary steering device uses hydraulic pressure, but an Electronic Power Steering (EPS) system adapted to transmit a rotation output of an electric motor to a steering shaft via a speed reduction mechanism has been increasingly employed these days from a viewpoint of a reduction in engine load, a reduction in weight, an enhanced steering stability and a quick restoring force.
The EPS system is configured such that an Electronic Control Unit (ECU) drives a motor in response to steering conditions and driver manipulation information detected by a speed sensor, a torque sensor and an angle sensor to enhance a steering stability and provide a quick restoring force, whereby a driver can safely steer a vehicle.
The speed sensor is a device detecting a running speed of a running vehicle, the torque sensor is a device outputting an electric signal in proportion to a torque detected by applying a torque to a steering shaft, and the angle sensor is a device outputting an electric signal in proportion to a rotation angle of a steering column.
Meanwhile, the torque sensor is configured in such a manner that at least two magnetic devices are used to measure a torque applied to the steering column, whereby, even if one magnetic device is out of order or develops an erroneous operation, another magnetic device is operated at a normal state. This configuration however suffers from a disadvantage in that the torque sensor becomes voluminous, and each magnetic device must be individually mounted on a printed circuit board.
Meantime, a torque angle sensor is such that a rotor and a stator are provided inside a case, and the torque angle sensor includes a main gear mounted on the rotor and at least two sub-gears meshed with the main gear. A magnet is arranged along a periphery of the rotor in the torque sensor, and a stator having a salient piece corresponding to a polarity of the magnet is arranged on the periphery, whereby a magnetic charge is detected in response to a difference of mutual revolutions between the magnet and the stator to thereby detect a torque of an input shaft and an output shaft, which is then transmitted to the ECU.
In case of the angle sensor, a driver rotates a steering wheel to cause a difference of rotation angles between the steering column and a driving shaft to be generated by rotation of the main gear attached to the steering column in association with the rotation with the steering column, at which time, the magnetic device recognizes a magnetic field of a magnet attached to the sub-gears meshed to the main gear and a rotational direction and transmits a signal thereof to the ECU. Generally, an AMR IC and a Hall IC are widely used for a magnetic device.
Meanwhile, in case of a conventional angle sensor where revolution of a sub-gear for each revolution of a main gear is approximately two revolutions, a maximum error for each rotation of the sub-gear is approximately one degree, and therefore, there is a need of installing at a controller an algorithm capable of reducing an influence by angle non-linearity outputted by the angle sensor, and as a result, there is a need of developing an angle sensor capable of minimizing the error.